So that just happened to me yesterday! let’s talk about it!
We had to connect one EX4200 switch to another EX4200 switch via the SFP port.
Now as you may know, the EX4200 had a 10gig SFP port , and we only had a 1000BASE-LX SFP Transceiver module (FTRJ1319P1BTL) . pluging that transceiver into the SFP port , but the port does not go up , no light , and when showing the interface we receive the following error: ‘device not found’ .
So, the temporary solution was, is to change the operating mode of the SFP port, using the following command:
# set chassis fpc 0 pic 1 sfpplus pic-mode 1g